Grounding protection method for low-voltage side of photovoltaic boost Huazi box-type transformer substation

Abstract

The invention discloses a ground protection method for a low-voltage side of a photovoltaic boost Huazi box transformer substation, and belongs to the technical field of photovoltaic boost Huazi box transformer substations, and the method comprises the following steps: obtaining a low-voltage side circuit of the photovoltaic boost Huazi box transformer substation, the low-voltage side circuit comprising a main loop, and a PLC control loop and a plurality of branch loops connected with the main loop; a voltage transformer module is arranged at the joint of the transformer low-voltage side main loop, the PLC control loop and each branch loop; zero-sequence current transformers are respectively arranged between the second circuit breakers of the branch loops and the cable terminals; if the secondary opening voltage is not zero, the measurement and control device is used for receiving the zero-sequence voltage and carrying out background alarm; and taking the branch loop of which the current value is not zero as a grounding fault line, and controlling a molded case circuit breaker of the fault line to perform protection tripping through a measurement and control device. According to the invention, the problem that the existing Huai-type box transformer substation cannot accurately determine the line with the grounding fault is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaic boost Chinese-style box-type transformers, and in particular relates to a grounding protection method for a low-voltage side of a photovoltaic boost Chinese-style box-type transformer. Background Art

[0002] Conventional Chinese box-type transformers, because the frame circuit breaker is located on the power supply side, when a single-phase grounding fault occurs on the low-voltage side line, the frame circuit breaker position side cannot collect the grounding capacitance current, nor can it determine the line grounding fault situation, and thus cannot achieve grounding protection tripping. Long-term operation with single-phase grounding on the low-voltage side line will cause line phase short circuit and low-voltage plastic shell burning, and the long-term existence of single-phase grounding faults is prone to develop into phase short circuits or multi-point grounding.

[0003] The existing Chinese-style box-type transformer can only rely on the overvoltage protection technology of measurement and control to achieve grounding protection. However, there are many situations that can cause line overvoltage, not only grounding faults, but also line overvoltage. It is impossible to determine which plastic shell has a grounding fault, and thus it is impossible to determine the specific line where the grounding fault occurs. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a grounding protection method for the low-voltage side of a photovoltaic boost Chinese-style box-type transformer, which solves the problem that the existing Chinese-style box-type transformer cannot accurately determine the specific line where a grounding fault occurs.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] The present invention provides a grounding protection method for the low-voltage side of a photovoltaic boost Chinese-type box-type transformer, comprising the following steps:

[0007] S1. Obtain a low-voltage side circuit of a photovoltaic booster transformer, wherein the low-voltage side circuit includes a main circuit, a PLC control circuit connected to the main circuit, and several branch circuits;

[0008] S2. Set the voltage transformer module to the connection between the main circuit on the low-voltage side of the transformer and the PLC control circuit and each branch circuit;

[0009] S3. A zero-sequence current transformer is respectively arranged between the second circuit breaker of each branch circuit and the cable terminal;

[0010] S4. Obtain the secondary open voltage of the voltage transformer when the photovoltaic booster transformer is working. If the secondary open voltage is not 0, use the measurement and control device to receive the zero-sequence voltage and issue a background alarm;

[0011] S5. Obtain the current value of the zero-sequence current transformer in each branch circuit, and regard the branch circuit with a current value not equal to 0 as a grounding fault line, and control the molded case circuit breaker of the fault line through the measurement and control device to perform protective tripping.

[0012] The beneficial effects of the present invention are as follows: the present invention provides a grounding protection method for the low-voltage side of a photovoltaic boost Chinese-style box-type transformer, which realizes real-time monitoring of grounding faults by setting a voltage transformer module in the main circuit of the low-voltage side of the photovoltaic boost Chinese-style box-type transformer, and realizes accurate determination of the specific line where a single-phase grounding fault occurs by respectively setting a zero-sequence current transformer on each branch circuit, thereby reducing the time for on-site power outage investigation and achieving grounding protection for the low-voltage side of the photovoltaic boost Chinese-style box-type transformer.

[0013] Further, the main circuit in S1 includes a first group of three current transformers connected in parallel, a first circuit breaker, a second group of three current transformers connected in parallel, a first fuse and a surge protector; the PLC control circuit and each branch circuit include a second circuit breaker and a cable terminal;

[0014] The primary sides of the first group of three parallel current transformers are all connected to the low-voltage side of the transformer; the secondary sides of the first group of three parallel current transformers are all connected to the incoming line terminal of the first circuit breaker; the outgoing line terminal of the first circuit breaker is connected to the primary side of the second group of three parallel current transformers; the secondary sides of the second group of three parallel current transformers are connected to the incoming line terminal of the first fuse and are respectively connected to each branch circuit; the outgoing line terminal of the first fuse is connected to the input terminal of the surge protector; the output terminal of the surge protector is grounded; the incoming line terminal of the second circuit breaker in the PLC control circuit is connected to the incoming line terminal of the first fuse; the outgoing line terminal of the second circuit breaker in the PLC control circuit is connected to the cable terminal head, and the cable terminal head is externally connected to the corresponding PLC controller; the incoming line terminal of the second circuit breaker in each branch circuit is connected to the incoming line terminal of the first fuse; the outgoing line terminal of the second fuse in each branch circuit is connected to the cable terminal head, and the cable terminal head is externally connected to the corresponding inverter.

[0015] Furthermore, the first circuit breaker adopts a frame circuit breaker; the second circuit breaker adopts a molded case circuit breaker with electric operation.

[0016] The beneficial effects of adopting the above further scheme are: the main circuit adopts a frame circuit breaker, which can provide higher reliability and safety, effectively isolate faults, and ensure the stable operation of the power supply system, while the branch circuit adopts a molded case circuit breaker with electric operation function, which can monitor the circuit status in real time to prevent misoperation.

[0017] Further, the voltage transformer module in S2 includes a second fuse, a voltage transformer and a resistor;

[0018] The incoming line end of the second fuse is connected to one end of the first fuse; the outgoing line end of the second fuse is connected to the primary side of the voltage transformer; the neutral point of the voltage transformer is connected to one end of the resistor; the other end of the resistor is grounded; the secondary side of the voltage transformer is grounded using an open triangle connection method.

[0019] The beneficial effects of adopting the above further scheme are: setting a voltage transformer at the lower end of the frame can obtain voltage information, monitor grounding fault conditions, and set a detuning resistor at the neutral point, which can effectively reduce the potential difference of the ground potential and avoid direct grounding of the main circuit, thereby improving the safety of the system; the present invention adopts an open triangle connection method for grounding on the secondary side of the voltage transformer, which is suitable for the situation of neutral point grounding, can effectively reduce the zero-sequence current, and improve the reliability and safety of the system.

[0020] Furthermore, the primary side of the zero-sequence current transformer in S3 is connected to the outlet terminal of the second circuit breaker in the same branch circuit; and the secondary side of the zero-sequence current transformer is connected to the cable terminal.

[0021] The beneficial effect of adopting the above further scheme is: by adding a zero-sequence current transformer in the molded case branch circuit, the present invention can quickly locate the fault through the current transformer measurement results when a single-phase grounding fault occurs, thereby improving the accuracy and reliability of fault detection.

[0022] Other advantages of the present invention will be analyzed in more detail in subsequent embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 The present invention is a flowchart of the steps of a grounding protection method for the low-voltage side of a photovoltaic boost Chinese-type box-type transformer in an embodiment of the present invention.

[0025] Figure 2 The schematic diagram is a circuit diagram of the low voltage side of the photovoltaic booster transformer in an embodiment of the present invention.

[0026] Figure 3 The schematic diagram of the circuit for improving the grounding protection of the low-voltage side of the photovoltaic booster transformer in the embodiment of the present invention.

[0027] Figure 4 Schematic diagram of current distribution of a zero-sequence current transformer in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0029] In the photovoltaic step-up Chinese-style box-type transformer, due to the PID effect of the photovoltaic inverter communication box and other problems, the neutral point of the transformer cannot be directly grounded, so the transformer can only use the Dy11 or Yd11 connection group.

[0030] like Figure 1 As shown, in one embodiment of the present invention, the present invention provides a grounding protection method for the low-voltage side of a photovoltaic boost Chinese box-type transformer, comprising the following steps:

[0031] S1. Obtain a low-voltage side circuit of a photovoltaic booster transformer, wherein the low-voltage side circuit includes a main circuit, a PLC control circuit connected to the main circuit, and several branch circuits;

[0032] like Figure 2 As shown, the main circuit includes a first group of three current transformers connected in parallel, a first circuit breaker, a second group of three current transformers connected in parallel, a first fuse and a surge protector; the PLC control circuit and each branch circuit include a second circuit breaker and a cable terminal;

[0033] The primary sides of the first group of three parallel current transformers are all connected to the low-voltage side of the transformer; the secondary sides of the first group of three parallel current transformers are all connected to the incoming line terminal of the first circuit breaker; the outgoing line terminal of the first circuit breaker is connected to the primary side of the second group of three parallel current transformers; the secondary sides of the second group of three parallel current transformers are connected to the incoming line terminal of the first fuse and are respectively connected to each branch circuit; the outgoing line terminal of the first fuse is connected to the input terminal of the surge protector; the output terminal of the surge protector is grounded; the incoming line terminal of the second circuit breaker in the PLC control circuit is connected to the incoming line terminal of the first fuse; the outgoing line terminal of the second circuit breaker in the PLC control circuit is connected to the cable terminal head, and the cable terminal head is externally connected to the corresponding PLC controller; the incoming line terminal of the second circuit breaker in each branch circuit is connected to the incoming line terminal of the first fuse; the outgoing line terminal of the second fuse in each branch circuit is connected to the cable terminal head, and the cable terminal head is externally connected to the corresponding inverter.

[0034] The first circuit breaker adopts a frame circuit breaker; the second circuit breaker adopts a molded case circuit breaker with electric operation.

[0035] In this solution, frame circuit breakers are used in the main circuit, which can provide higher reliability and safety, effectively isolate faults, and ensure the stable operation of the power supply system; molded case circuit breakers with electric operation functions are used in branch circuits, which can monitor the circuit status in real time to prevent misoperation.

[0036] like Figure 3 As shown, S2, a voltage transformer module is set to the connection between the main circuit of the low-voltage side of the transformer and the PLC control circuit and each branch circuit;

[0037] The voltage transformer module includes a second fuse, a voltage transformer and a resistor;

[0038] The incoming line end of the second fuse is connected to one end of the first fuse; the outgoing line end of the second fuse is connected to the primary side of the voltage transformer; the neutral point of the voltage transformer is connected to one end of the resistor; the other end of the resistor is grounded; the secondary side of the voltage transformer is grounded using an open triangle connection method.

[0039] In this solution, the voltage transformer is set at the lower end of the frame to measure the voltage of the low-voltage circuit and obtain voltage information; a resistor is set at the neutral point as a detuning resistor, which can effectively reduce the ground potential difference and avoid direct grounding of the main circuit, thereby improving the safety of the system; an open triangle connection method is used on the secondary side of the voltage transformer for grounding, which is suitable for the case of neutral point grounding, can effectively reduce the zero-sequence current and improve the reliability and safety of the system.

[0040] The voltage transformer has a transformation ratio of 0.8 / √3 / 0.1 / 3, a protection level of 3P, and a capacity of 10VA.

[0041] In this scheme, the voltage transformer has multiple secondary sides, namely 0.8, √3, 0.1, and 3, with a total of 3 phases. Among them, 0.8 and √3 are two secondary sides, 0.1 is the secondary side of the neutral point, and 3 is the zero-sequence side.

[0042] like Figure 3 As shown, S3, a zero-sequence current transformer is respectively arranged between the second circuit breaker of each branch circuit and the cable terminal head;

[0043] The primary side of the zero-sequence current transformer is connected to the outlet terminal of the second circuit breaker in the same branch circuit; the secondary side of the zero-sequence current transformer is connected to the cable terminal.

[0044] In this solution, by adding a zero-sequence current transformer in the molded case branch circuit, the fault can be quickly located through the current transformer measurement results when a single-phase grounding fault occurs, thereby improving the accuracy and reliability of fault detection.

[0045] The solution of the present invention selects suitable circuit breaker types in the main circuit and each branch circuit, combines measures such as voltage transformers and detuning resistors, ensures the safety and reliability of the system, and enhances the fault detection capability through zero-sequence current transformers.

[0046] S4. Obtain the secondary open voltage of the voltage transformer when the photovoltaic booster transformer is working. If the secondary open voltage is not 0, use the measurement and control device to receive the zero-sequence voltage and issue a background alarm;

[0047] In this embodiment, under normal circumstances, the secondary opening voltage of the voltage transformer is 0. If a single-phase grounding fault occurs, the secondary side voltage is 100V.

[0048] S5. Obtain the current value of the zero-sequence current transformer in each branch circuit, and regard the branch circuit with a current value not equal to 0 as a grounding fault line, and control the molded case circuit breaker of the fault line through the measurement and control device to perform protective tripping.

[0049] like Figure 4As shown, in a practical example of the present invention, under normal circumstances, the current of the zero-sequence circuit transformer is 0, that is, the three-phase vector sum is 0. When single-phase grounding occurs in phase A, the capacitance currents of B and C relative to ground are I1 and I2, and the capacitance currents of the remaining loops B and C relative to ground are I3-I6. The current vector sum of the zero-sequence current transformer TAN1 is I1+I2-(I1+I2+I3+I4+I5+I6)+I3+I4+I5+I6-(I3+I4+I5+I6)=(I3+I4+I5+I6), and the current is not 0. At this time, the measurement and control monitors which zero-sequence current is generated, and then determines which line the grounding fault point is in, and controls the molded case circuit breaker to perform protection tripping through measurement and control, thereby realizing single-phase grounding protection.

[0050] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A grounding protection method for the low-voltage side of a photovoltaic boost Chinese box-type transformer, characterized in that: The steps include: S1. Obtain a low-voltage side circuit of a photovoltaic booster transformer, wherein the low-voltage side circuit includes a main circuit, a PLC control circuit connected to the main circuit, and several branch circuits; S2. Set the voltage transformer module to the connection between the main circuit on the low-voltage side of the transformer and the PLC control circuit and each branch circuit; S3. A zero-sequence current transformer is respectively arranged between the second circuit breaker of each branch circuit and the cable terminal; S4. Obtain the secondary open voltage of the voltage transformer when the photovoltaic booster transformer is working. If the secondary open voltage is not 0, use the measurement and control device to receive the zero-sequence voltage and issue a background alarm; S5. Obtain the current value of the zero-sequence current transformer in each branch circuit, and regard the branch circuit with a current value not equal to 0 as a grounding fault line, and control the molded case circuit breaker of the fault line through the measurement and control device to perform protective tripping.

2. The grounding protection method for the low-voltage side of a photovoltaic boost Chinese-type box-type transformer according to claim 1 is characterized in that: The main circuit in S1 includes a first group of three current transformers connected in parallel, a first circuit breaker, a second group of three current transformers connected in parallel, a first fuse and a surge protector; the PLC control circuit and each branch circuit include a second circuit breaker and a cable terminal; The primary sides of the first group of three parallel current transformers are all connected to the low-voltage side of the transformer; the secondary sides of the first group of three parallel current transformers are all connected to the incoming line terminal of the first circuit breaker; the outgoing line terminal of the first circuit breaker is connected to the primary side of the second group of three parallel current transformers; the secondary sides of the second group of three parallel current transformers are connected to the incoming line terminal of the first fuse and are respectively connected to each branch circuit; the outgoing line terminal of the first fuse is connected to the input terminal of the surge protector; the output terminal of the surge protector is grounded; the incoming line terminal of the second circuit breaker in the PLC control circuit is connected to the incoming line terminal of the first fuse; the outgoing line terminal of the second circuit breaker in the PLC control circuit is connected to the cable terminal head, and the cable terminal head is externally connected to the corresponding PLC controller; the incoming line terminal of the second circuit breaker in each branch circuit is connected to the incoming line terminal of the first fuse; the outgoing line terminal of the second fuse in each branch circuit is connected to the cable terminal head, and the cable terminal head is externally connected to the corresponding inverter.

3. The grounding protection method for the low-voltage side of a photovoltaic boost Chinese-type box-type transformer according to claim 2 is characterized in that: The first circuit breaker adopts a frame circuit breaker; the second circuit breaker adopts a molded case circuit breaker with electric operation.

4. The grounding protection method for the low-voltage side of a photovoltaic boost Chinese-type box-type transformer according to claim 2 is characterized in that: The voltage transformer module in S2 includes a second fuse, a voltage transformer and a resistor; The incoming line end of the second fuse is connected to one end of the first fuse; the outgoing line end of the second fuse is connected to the primary side of the voltage transformer; the neutral point of the voltage transformer is connected to one end of the resistor; the other end of the resistor is grounded; the secondary side of the voltage transformer is grounded using an open triangle connection method.

5. The grounding protection method for the low-voltage side of a photovoltaic boost Chinese-type box-type transformer according to claim 3 is characterized in that: The primary side of the zero-sequence current transformer in S3 is connected to the outlet terminal of the second circuit breaker in the same branch loop; the secondary side of the zero-sequence current transformer is connected to the cable terminal.

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